This invention relates generally to the field of aircraft and, more specifically, to systems and methods for controlling aircraft.
Aircraft generally have a variety of control surfaces that can be deflected to cause the aircraft to perform maneuvers during flight. FIG. 1 illustrates an aircraft 8 having typical control surfaces. Aircraft 8 includes an airframe 10, a first wing 13, a second wing 16, and a rudder 19. Movably coupled to first wing 13 is a flap 14 and an aileron 15, and movably coupled to second wing 16 is a flap 17 and an aileron 18. Flap 14 and flap 17 can be extended from the trailing edge of first wing 13 and second wing 16, respectively, to generate increased lift for aircraft 8, which can cause aircraft 8 to climb. Aileron 15 and aileron 18, on the other hand, are hingedly coupled to first wing 13 and second wing 16, respectively, and can be deflected relative to the trailing edge of first wing 13 and second wing 16, respectively, to generate increased or decreased lift. Because of their distance from a centerline 11 of aircraft 8, the increased or decreased lift generated by deflecting aileron 15 or aileron 18 can readily cause aircraft 8 to rotate about centerline 11, i.e., a roll maneuver. For example, deflecting aileron 15 downward generates increased lift, and deflecting aileron 18 upward generates decreased lift, which together can cause aircraft 8 to roll in the direction of arrow 12. In general, aileron 15 and aileron 18 can be deflected simultaneously, albeit in opposite directions, or individually to cause aircraft 8 to roll in either direction. Note, aileron 15 and aileron 18 can also be used in making turns, especially coordinated turns. In addition, rudder 19 can be deflected to turn aircraft 8 either left or right, i.e., a yaw maneuver. Rudder 19, however, can also be used during roll maneuvers, as discussed below.
FIG. 2 is a plot illustrating the relation between the coefficient of drag and the coefficient of lift for first wing 13 and second wing 16 based on the deflection of aileron 15 and aileron 18, respectively. Note, the coefficient of lift and the coefficient of drag are converted to actual lift and drag forces by multiplying the coefficients by the area of the surface and the square of the velocity. When aircraft 8 is flying level, aileron 15 and aileron 18 are typically set so that first wing 13 and second wing 16 have substantially equally coefficients of lift and drag, represented by point 15U and point 18U, respectively, allowing aircraft 8 to be balanced in roll moment and yaw moment. When aircraft 8 is to execute a roll maneuver, however, the coefficient of lift and the coefficient of drag for first wing 13 and second wing 16 change, due to the deflection of aileron 15 and aileron 18, respectively. For example, when aircraft 8 is to roll in the direction of arrow 12 in FIG. 1, aileron 15 deflects downward, causing the coefficient of lift to increase and a consequent increase in the coefficient of drag, represented by point 15DD, and aileron 18 deflects upward, causing the coefficient of lift to decrease and a consequent decrease in the coefficient of drag, represented by point 18DU. The increased lift generated by the deflection of aileron 15 and the decreased lift generated as a consequence of the deflection of aileron 18 cause aircraft 8 to roll in the direction of arrow 12. However, the increased drag generated as a consequence of the deflection of aileron 15 and the decreased drag generated as a consequence of the deflection of aileron 18 produce a moment that causes aircraft 8 to yaw in the direction of first wing 13, i.e., away from the roll, termed xe2x80x9cadverse yaw.xe2x80x9d
Typically, an adverse yaw moment is not problem because aircraft have control surfaces, such as rudders or differential drag flaps, to compensate for the induced yaw moment. Rudder 19 of aircraft 8, for example, may be deflected to compensate for an induced yaw moment. But in aircraft that have no such control surfaces, or prefer not to use them due to radar cross section concerns, compensating for either adverse yaw moment or its opposite, i.e., proverse yaw moment, during a roll maneuver becomes more difficult.
The present invention provides a system and method that substantially reduces or eliminates at least some of the disadvantages and problems associated with previously developed aircraft control surfaces. Accordingly, in certain embodiments, the present invention provides a system and method that compensate for yaw moment during at least certain roll maneuvers of an aircraft without the use of a rudder or differential drag flaps.
In particular embodiments, a system in accordance with the present invention includes an airframe, a first airfoil, and a second airfoil. The first airfoil is coupled to a first side of the airframe, and the second airfoil is coupled to a second side of the airframe, at least a portion of the first airfoil and at least a portion of the second airfoil being controllably deflectable to facilitate roll maneuvers of the aircraft. The deflectable portion of the first airfoil is deflectable to generate increased lift and a consequent increased drag for at least a portion of the first airfoil, and the deflectable portion of the second airfoil is deflectable to generate negative lift and a consequent increased drag for at least a portion of the second airfoil during at least one roll maneuver, the increased lift of the first airfoil and the decreased lift of the second airfoil causing the aircraft to roll, and the increased drag of the second airfoil producing a yaw moment that counteracts the yaw moment produced by the increased drag of the first airfoil such that the roll maneuver does not substantially change the yaw moment of the aircraft.
In other embodiments, a method in accordance with the present invention includes deflecting at least a portion of a first airfoil to generate increased lift and a consequent increased drag for at least a portion of the airfoil to facilitate a roll maneuver and deflecting at least a portion of a second airfoil to generate negative lift and a consequent increased drag for at least a portion of the airfoil to facilitate the roll maneuver. The increased lift of the first airfoil and the decreased lift of the second airfoil generate a roll moment causing the aircraft to roll, and the increased drag of the second airfoil produces a yaw moment that counteracts the yaw moment produced by the increased drag of the first airfoil such that the roll maneuver does not substantially change the yaw moment of the aircraft.
The present invention has several technical features and advantages. For example, in particular embodiments, the invention allows an aircraft to perform a roll maneuver without substantially changing the yaw moment of the aircraft, which allows the aircraft to perform a roll maneuver without substantial adverse yaw. This ability may be particularly useful in making coordinated turns in aircraft where the design emphasis is on low radar cross section, because the use of rudders or differential drag flaps to compensate for adverse yaw increases radar cross section. As another example, in certain embodiments, the invention allows an aircraft to perform a roll maneuver without experiencing a substantial change in net lift, which prevents the aircraft from losing altitude during the maneuver. As an additional example, in some embodiments, the invention allows an aircraft to perform a roll maneuver without substantially changing the pitch moment of the aircraft, which prevents the aircraft from changing its longitudinal orientation during the maneuver. As a further example, in certain embodiments, the invention allows an aircraft to produce a yaw moment without substantially changing the roll moment. This could allow a pilot to line up the aircraft with the runway even if there is a crosswind. Furthermore, this could facilitate a more familiar feel to pilots who are accustomed to controlling yaw with rudder pedals. Moreover, in particular embodiments, the yaw maneuver may be executed without substantially changing the pitch moment or net lift of the aircraft. Note, some embodiments may possess none, one, some, or all of these technical features and advantages and/or additional technical features and advantages.
In particular embodiments, the aircraft has swept back wings. In some of these embodiments, a method and system in accordance with the present invention include the ability to deflect at least a portion of a first airfoil to generate increased lift and a consequent increased drag for at least a portion of the first airfoil and deflect at least a portion of a second airfoil to generate negative lift and a consequent increased drag for at least a portion of the second airfoil, wherein the fore-aft spacing of the lift forces is coincident during at least one roll maneuver. By aligning these forces, the aircraft is balanced in pitch during the roll maneuver and can still perform a coordinated roll, in that the increased lift generated by the first airfoil and the negative lift generated by the second airfoil produce a roll moment while the increased yaw moment produced by the increased drag of the first airfoil is countered by the increased yaw moment produced by the increased drag of the second airfoil.
Other technical features and advantages will be readily apparent to one of skill in the art from the following figures, description, and claims.